In this project two different calcium (Ca) channels from paramecia will be studied after they have been incorporated into planar lipid bilayers. The long term goals of this project are to understand at the molecular level how Ca channels work, how cells regulate the entry of Ca across the cell membrane via Ca channels, and how channels and channel regulation control cell function. Paramecia are the most primitive organism known to have voltage-dependent Ca channels. While paramecia have neither a cardiovascular nor a nervous system, its Ca channels seem to be similar to one class of Ca channels found in mammalian heart and nerve cells. The other channel of paramecia to be studied in a mechanoreceptor-associated (mechano) channel which is permeable only to divalent cations. This channel may be related to other pressure- and stretch-activated channels found in variety of cells. Paramecia channels were selected for study because paramecia have many features which make it particularly suitable to electrophysiological, biochemical, and genetic manipulations that would be more difficult in a mammalian system. In all the proposed experiments, channel activity will be monitored electrically after they have been incorporated into planar lipid bilayers. The specific experiments planned for the voltage-dependent Ca channel are: 1) to continue the testing of pharmacological agents for this channel with the hopes of finding a biochemical probe for the channel protein and of finding an agent that cross reacts with mammalian channels, 2) to investigate the mechanism of Ca-dependent inactivation, and 3) to identify the functional consequences of Ca channel alterations in mutant paramecia. The specific experiments planned for the mechano channel are 1) to verify that this channel is mechanically activated and 2) to test the generality of an ion permeation model that was developed for a different type of Ca channel.